The invention relates to image creation systems and more specifically to color information synthesis suitable for use in such systems.
There are a number of standard computer peripherals available that permit "computer graphics" to be generated entirely electronically. These can take the form of vector or raster displays with the input device usually in the form of a touch tablet on which the operator can draw and see the results of this work in real time on the electronic display.
A typical known electronic graphics system is shown in FIG. 1, the main components comprising a touch tablet 10, a computer 12, a frame store 13 and a display 17. An artist draws with the stylus 11 of the touch tablet and the computer 12 registers the coordinates of the stylus whilst remembering the selected color from selector 18 with which the artist has chosen to draw. The computer then feeds the appropriate addresses to the frame store 13 where the pixel at that address is modified to hold the code (typically 8 bits) corresponding to the chosen color which it receives as incoming data. As the frame store is read at normal broadcast video rates under the control of the display address generator 15 typically locked to an external synchronizing reference if available, then the lines, or pictures, drawn by the artist become visible on the display. The monitor 17 is shown receiving the picture data converted into analogue form via DAC 14. It is found in practice that, providing the display is near to the touch tablet, the fact that the artist is not watching his hand but the screen provides no problem.
It is possible to use the computer to designate the stylus size via selector 19 so as to be several picture points in diameter for example so that the lines on the `drawn` image will be of a designated width, as though drawn with a larger stylus. This is achieved by controlling the writing of data into the frame store so that adjacent picture points receive the incoming data also.
Although the system shows a single frame store 13 for ease of understanding, in practice the color information from computer 12 would typically be passed to three separate frame stores each handling respectively the luminance and color difference components of the color information (Y,I and Q for NTSC) and their outputs would be recombined to produce the normal color information displayed on monitor 17 using standard video techniques. Alternative systems using a single frame store are known where `partial color` is handled in the form of the Red, Green and Blue components of the color information. Although the color is shown simply as being selected by selector 18, alternatively the operator, when he desires to chose a color, can call up an array of cells onto the monitor screen equivalent to a number of `paint pots` and by moving the stylus over the touch tablet area can view the corresponding stylus position on the screen (as the computer typically generates a cross-wire or other screen cursor identifying the stylus position). When the stylus is located over the desired `paint pot`, the tablet is actually touched which then ensures that this is the color selected by the computer for output to screen via the frame store as the stylus draws the desired image.
A problem with such systems especially where greater realism and more color variations are desired is that the system must be designed to have a large number of such `paint pots` available to the operator. Even then, the operator may find that the selection available is still not adequate for his needs.
The present invention is directed to an arrangement which allows the operator to produce any of a large variety of colors without the need to have unwieldy numbers of paint pots or other color selector mechanisms.
The term `color` is used throughout the patent specification to encompass not only different colors but different hues of the same color as well as different shades of grey in the monochrome medium.